Saturday's Proms both aimed at changing the way we think. The afternoon found Cameron Carpenter redefining the organ recital in terms of glamorous virtuosity. Playing in spangled pants and a cut-off T shirt, he looked like a rock star. Talking between pieces to the BBC announcer, he defined his feelings for his instrument in Byronic terms as "passion or obsession", but quite definitely "not love".

Revelations of a different order came in the evening, when Riccardo Chailly and the Leipzig Gewandhaus undertook a reappraisal of Mendelssohn, the most famous kapellmeister in the orchestra's history. Chailly's argument is that Mendelssohn was a more troubled figure than is usually believed, and that his apparent facility in composition was undermined by self-doubts that led him to excessive revision of his own work .

His posthumously published Fifth, or "Reformation" Symphony lost an entire movement when the orchestra entrusted with the premiere turned against it. Chailly presented us with the original score, together with the Violin Concerto – Nikolaj Znaider was the sensational soloist – and early versions of the overtures Ruy Blas and The Fair Melusine. I'm not sure that the restored music, though beautiful, makes the Fifth a masterpiece, though Chailly made the strongest case for it. Hearing the Gewandhaus, though, was a privilege: no other orchestra plays Mendelssohn half as well.

• If you're at any Prom this summer, tweet your thoughts about it to @guardianmusic using the hashtag #proms and we'll pull what you've got to say into one of our weekly roundups – or leave your comments below.